The effect of herbicides on the root system of wheat plants

Three commercial herbicides, at the rates normally recommended for selective weed control in cereal crops, deformed the roots of spring wheat plants grown in sand culture. Affected roots produced large numbers of short swollen lateral branches which later grew on to form tassel-like bundles of side roots. Only the mecoprop and MCPA components of the mixtures were responsible for the deformities; ioxynil and dicamba had no effect. Mecoprop applied to the rooting medium severely deformed the roots but foliar application also resulted in some abnormalities. The effects of the herbicides on root and shoot dry weights were not correlated with their deformative effects.     

Simulation of the effect of root distribution on hydraulic redistribution in a desert riparian forest

Hydraulic redistribution (HR) of roots plays an important role in the water relations of desert riparian plants. In order to estimate the effect of vertical root distribution on the HR process of Populus euphratica Oliv. during the entire growth season, we performed simulation and scenario analyses based on the observed soil water potential and root distribution data. The results showed that our simulation model achieved a good accuracy. The initial value of soil water content could significantly affect the simulated soil water content at soil depths of >90 cm, but had only limited effect on soil water content in the 0- to 90-cm soil layers. Scenario analysis revealed that with increase in root distribution depth, the HR process extended from the upper and middle soil layers downward toward the middle and deeper soil layers: the deeper the root distribution, the more likely it was to trigger the HR process in deep soil layers. However, a deeper rooting system led to a decrease in the total amount of hydraulically redistributed water over the entire soil column. Redistributed water also significantly increased the soil water depletion and the soil water storage. However, the effects of redistributed water (HR vs. without HR) on water depletion and soil water storage were reduced with the deepening of root distribution. These results indicate that HR can obviously affect the moisture of the upper soil layers, while vertical root distribution significantly changes the spatial and quantitative characteristics of HR within soil columns.     

Earthworm effect on root morphology in a split root system

Plants respond to their environment through adaptations such as root proliferation in nutrient-rich patches. Through their burrows and casts production in soil, earthworms create heterogeneity which could lead to local root adaptations or systemic effects. To investigate the effect of earthworms on root system morphology and determine whether earthworm effect is local or systemic, we set up two independent split root experiments with rice or barley, (i) without earthworm (CC), (ii) with earthworms in both compartments (EE), and (iii) with earthworms in one single compartment (CE). Earthworms had an effect on belowground plant biomass. The relative length of thick roots decreased with an increasing abundance of earthworms. Some root diameter classes responded to earthworm number in a linear or curvilinear way, making simple conclusions difficult. We found no difference in root biomass or morphology between the two compartments of the split root system in the CE treatment, but a positive effect of earthworm biomass on root biomass, volume, surface area, and length at the whole plant level. Results supported a systemic effect dependent on earthworm abundance. Modification of nutrient mineralization, soil physical structure, and/or the concentration of signal molecules could all be responsible for this systemic effect.     

Competing neighbors: light perception and root function

The literature reveals opposing views regarding the importance of intrinsic population regulation in mammals. Different models have been proposed; adding importance to contrasting life histories, body sizes and social interactions. Here we evaluate current theory based on results from two Scandinavian projects studying two ecologically different mammal species with contrasting body sizes and life history traits: the root vole Microtus oeconomus and the brown bear Ursus arctos. We emphasize four inter-linked behavioral aspects—territoriality, dispersal, social inhibition of breeding, and infanticide—that together form a density-dependent syndrome with potentially regulatory effects on population growth. We show that the two species are similar in all four behaviors and thus the overall regulatory syndrome. Females form matrilineal assemblages, female natal dispersal is negatively density dependent and breeding is suppressed in philopatric young females. In both species, male turnover due to extrinsic mortality agents cause infanticide with negative effects on population growth. The sex-biased and density-dependent dispersal patterns promote the formation of matrilineal clusters which, in turn, leads to reproductive suppression with potentially regulatory effects. Hence, we show that intrinsic population regulation interacting with extrinsic mortality agents may occur irrespective of taxon, life history and body size. Our review stresses the significance of a mechanistic approach to understanding population ecology. We also show that experimental model populations are useful to elucidate natural populations of other species with similar social systems. In particular, such experiments should be combined with methodical innovations that may unravel the effects of cryptic intrinsic mechanisms such as infanticide.     

The effect of semi-dwarf genes on root system size in field-grown barley

Root system size (RSS) was measured in 12 diverse barley genotypes and 157 double-haploid lines (DHs), using electric capacitance. The parents of the DHs, Derkado and B83-12/21/5, carry different semi-dwarfing genes, sdw1 and ari-e.GP, respectively. Estimates of RSS were taken in the field thrice during plant development: stem elongation (RSS1), heading (RSS2) and grain filling (RSS3). The 12 barley genotypes were assessed over 3 years and at two or three locations each year; the DH mapping population was assessed at two locations in 2002. Among the 12 barley genotypes, those with the semi-dwarf genes had greater RSS values in all 3 years (28.9, 24.6 and 15.0% in years 1, 2 and 3, respectively) compared to non-semi-dwarf controls. The DH population showed transgressive segregation on both sides of the parent means, indicating polygenic control of RSS. Quantitative trait loci (QTLs) for RSS were found on five of the seven chromosomes: 1H, 3H, 4H, 5H and 7H and these were compared with previously mapped agronomic traits. The TotalRSS QTL on 3H was associated with sdw1 and QTLs for height, plant yield and plant weight. The RSS3 QTL on 5H was associated with ari-e.GP and QTLs for height, plant yield, plant weight, harvest index and tiller number. The RSS3 QTL on 7H was also associated with a TotalRSS QTL and QTLs for plant weight and harvest index. Other RSS QTLs were not associated with any other trait studied. RSS is considered to be a polygenic trait linked to important traits, in particular to yield. The study highlights the effects of semi-dwarfing genes and discusses the potential for breeding for root traits.     

Crop root behavior coordinates phosphorus status and neighbors: from field studies to three-dimensional in situ reconstruction of root system architecture

Root is a primary organ to respond to environmental stimuli and percept signals from neighboring plants. In this study, root responses in maize (Zea mays)/soybean (Glycine max) intercropping systems recognized soil phosphorus (P) status and neighboring plants in the field. Compared to self culture, the maize variety GZ1 intercropping with soybean HX3 grew much better on low P, but not in another maize variety, NE1. This genotypic response decreased with increasing distance between plants, suggesting that root interactions were important. We further conducted a detailed and quantitative study of root behavior in situ using a gel system to reconstruct the three-dimensional root architecture. The results showed that plant roots could integrate information on P status and root behavior of neighboring plants. When intercropped with its kin, maize or soybean roots grew close to each other. However, when maize GZ1 was grown with soybean HX3, the roots on each plant tended to avoid each other and became shallower on stratified P supply, but not found with maize NE1. Furthermore, root behavior in gel was highly correlated to shoot biomass and P content for field-grown plants grown in close proximity. This study provides new insights into the dynamics and complexity of root behavior and kin recognition among crop species in response to nutrient status and neighboring plants. These findings also indicate that root behavior not only depends on neighbor recognition but also on a coordinated response to soil P status, which could be the underlying cause for the different growth responses in the field.     

Development of the musculoskeletal system: meeting the neighbors

In March 2011, researchers met for the second Batsheva Seminar on Integrative Perspectives on the Development of the Musculoskeletal System. This meeting was a unique opportunity for researchers working on muscle, connective tissue, tendons, ligaments and bone to discuss the development of the musculoskeleton, recognizing that it is an integrated, functional system. The talks and discussions at this meeting highlighted that interactions between the different tissue components are crucial for musculoskeletal morphogenesis.     

The effect of Heterodera avenae, on the root system of susceptible and resistant oat seedlings

The effects of invasion by the cereal cyst nematode, Heterodera avenae, on the root growth of susceptible and resistant oat seedlings were similar. Nematode invasion directly inhibited root extension and lateral root production, which was dependent upon the developmental status of the invaded root tissue and the nematode density cm-¹ root. Both responses are caused by mechanical damage due to nematode invasion leading to decreased top growth in the host. Reduced root development, decreased efficiency of water and nutrient uptake in invaded plants being indirect effects of nematode invasion.     

The effect of root excretions on Azotobacter

Изучалося влияние корневых выделений ячменя и пшеницы, а также их фракций, на рост и фиксацию молекулярного азота азотобактером. Было установлено, что корневые выделения ячменя и пшеницы могут—в зависимости от условий культивирования— служить для азотобактера источником углерода. При условии аэрации или перемешивании культивационной среды азотобактер способен очень хорошо использовать корневыея выделени ячменя и пшеницы в качестве единственного источника углерода, но в стационарных условиях культивирования в присутствии этих выделений азотобактер— в зависимости от штамма—растет очень слабо или вовсе не растет. И в присутствии глюкозы в перемешиваемой культуре даже 1,5% концентрация корневых выделенийстимулирует рост азотобактера, тогда как в стационарной культуре его рост резко подавляется даже в 10 раз более низкими концентрациями. В стационарной среде с глюкозой корневые выделения стимулируют фиксацию молекулярного азота азотобактером вплоть до концентрации 0,05% этих выделений, тогда как при более высоких концентрациях наблюдается угнетение фиксации азота. Изучение фракции органических кислот, аминокислот и сахаров из корневых выделений ячменя и пшеницы показало, что лучше всего используется фракция органических кислот. В их присутствии в среде азотобактер растет без ?лаг”-фазы. Из фракции сахаров в выделениях корней исследуемый штамм азотобактера лучше всего использовал галактозу и фруктозу. Он хорошо рос также в присутствии глюкозы и мальтозы, тогда как в присутствии пентоз и метилированных сахаров он рос слабо. Если в культивационной среде имелись фракции аминокислот из выделений корней ячменя и пшеницы, азотобактер в перемешиваемой культуре рос хорошо, но в стационарной культуре почти не рос. В присутствии глюкозы и фракции аминокислот в перемешиваемой культуре наблюдается стимулирование роста, в особенности в начальных его фазах, в стационарных же условиях культивирования фракция аминокислот угнетает и рост, и фиксацию молекулярного азота. Стимулирующее действие аминокислотной фракции на рост азотобактера в начальных стадиях культивировании при перемешивании можно обьяснить влиянием аминокислот, содержащих серу и находящихся в выделениях корней ячменя и пшеницы. Сравнение влияния на рост фракции аминокислот в различных условиях культивирования с влиянием корневых выделений и фракции сахаров и органических кислот показывает, что в выделениях корней ячменя и пшеницы имеются также угнетающие вещества, присутствующие в фракции амниокислот, термолабильные и полностью проявляющиеся только в статических условиях культивирования. В условиях аэрации или перемешивания культуры азотобактер в их присутствии может хорошо произрастать.     

Increased root oxygen uptake in pea plants responding to non-self neighbors

Recent studies have demonstrated that plants alter root growth and decrease competition with roots of the same individual (self); however, the physiological traits accompanying this response are still widely unknown. In this study, we investigated the effect of root identity on gas exchange in the model species pea (Pisum sativum L.). Split-root plants were planted so that each pot contained either two roots of the same plant (self) or of two different plants (non-self), and the responses of biomass, photosynthesis, and respiration were measured. The photosynthetic rate was not affected by the identity of the root neighbor. We found a reduction of leaf dark respiration by half, accompanied by an increase in nocturnal root respiration by 29 % in plants neighboring with non-self. The activity of the alternative oxidase (AOX) pathway increased when plants responded to non-self neighbors. The increased activity of AOX in plants responding to non-self indicates carbon imbalances in roots, possibly as a consequence of increased root exudation and communication between individuals. If such an effect occurs more widely, it may change the assumptions made for the quantity of respiration as used in carbon budget models.     

The effect of irrigation regimes on plum (Prunus cerasifera) root system development dynamics

Prunus genus species are widely spread in semi-arid regions due to their ability to adjust to the limited water supply. Former research described the effect of water deficit on their aboveground development. However, less is known about the effects of water stress on the development of the root system. In order to investigate the effects of the irrigation regime on the root system development, young plum (Prunus cerasifera) trees were grown under three irrigation regimes for a period of five months. The effects of the irrigation regime on different root order and total root system elongation, biomass growth and tip numbers were analyzed. The results indicate that the responses vary according to the stress level. Under moderate stress, the total root system biomass decreases relative to the full irrigation treatment. However, low-order root formation remains similar to that found under no stress conditions. Under severe stress, the formation of low-order roots is also inhibited. Our results suggest that plum trees’ response to water deficit stress escalates according to the stress level. Namely, moderate stress affects the growth rate of the root system but does not alter the relative contribution of different orders, while severe stress both inhibits the total growth and changes the relative contribution of the different root orders. The combined measurements of the total root system and the different orders enable the identification of a stepwise response to water stress.     

The dependence of root system properties on root system biomass of 10 North American grassland species

Dependence of the properties of root systems on the size of the root system may alter conclusions about differences in plant growth in different environments and among species. To determine whether important root system properties changed as root systems aged and accumulated biomass, we measured three important properties of fine roots (tissue density, diameter, and C:N) and three biomass ratios (root:shoot, fine:coarse, and shallow:deep) of monocultures of 10 North American grassland species five times during their second and third years of growth. With increasing belowground biomass, root tissue density increased and diameter decreased. This may reflect cortical loss associated with the aging of roots. For non-legumes, fine root C:N decreased with increasing root biomass, associated with decreases in soil solution NO^{3 –} concentrations. No changes in fine root C:N were detected with increasing belowground biomass for the two legumes we studied. Among all 10 species, there were generally no changes in the relative amounts of biomass in coarse and fine roots, root:shoot, or the depth placement of fine roots in the soil profile as belowground biomass increased. Though further research is needed to separate the influence of root system size, age of the roots, and changes in nutrient availability, these factors will need to be considered when comparing root functional traits among species and treatments.     

Patterns of root architecture adaptation of a phreatophytic perennial desert plant in a hyperarid desert

Plant root systems can respond to nutrient availability and distribution by changing the three-dimensional deployment of their root architecture. The year after year variation of root architecture was investigated in a perennial phreatophyte in the controlled condition vegetation situated in the oasis in the Chinese Taklamakan desert with the goal to elucidate their adaptation to hyperarid environment. The whole plants of an indigenous perennial legume Alhagi sparsifolia Shap. with intact root systems were excavated at the end of each growing season from 2007 to 2009 and analyzed for architecture, above and belowground biomass, root/shoot ratio, root depth, seed yields and ramet. Changes in water availability were found to have stupendous effects on taproot depth, lateral root length and ramet quantity. Relative to shoot dry weight, taproot depth decreased with increasing water availability. In contrast, lateral root elongation was promoted by higher water availability.We tested the hypothesis that (1) irrigation increases root biomass and the quantity of ramets, and (2) A. sparsifolia Shap. develops an efficient root architecture that could absorb soil water and nutrition.     

The effect of a desert climate on the lactation and on the fertility of the nursing rat

Forty white rats were raised and mated in a controlled environment at 22°C. Twelve hours after parturition they were mated and separated into two equal groups. One group (control) remained at 22°C whilst the second group(desert) was kept in an open shed during July (daily temperature range: 18 to 37°C). The rats were sacrificed at 18 days post partum. Control rats ate 25% more food than desert rats; water consumption was the same in both groups. Body weights were initially similar, but from 12 days post partum onwards, the control rats increased their body weight at a significantly higher rate than did the desert rats. Milk production, assessed by litter weight gains, was higher in control group rats. Body composition and organ weights were similar except for the gut of the control group which was heavier. The number of CORPORA LUTEA was significantly lower in the desert group as were conception rates and embryo numbers; the weight of individual embryos and the weight of embryo per dam were, however, significantly higher in the desert group. It was postulated that during early pregnancy, maternal weight and mammary tissue may have preference over the uterus for nutritional sources, whilst in later pregnancy the embryos may have preference.     

The effect of 5-azacytidine on the root meristem ofVicia faba

The primary roots ofVicia faba seedlings were placed in a solution of 5-azacytidine and their further growth was observed after being replaced in running tap water. No inhibition of elongation occurred during the action of the 10^?5 M solution of 5-azacytidine for 24 hours, but during subsequent cultivation in water in the absence of inhibitor, further growth was blocked. This inhibition could be overcome by cytidine, uridine, sodium azide, 5-azidomethyluracil and simultaneously with the 5-azacytidine solution. Inhibition was accompanied by a high incidence of chromosome stickiness and to a less extent by an incidence of chromosome aberrations. The occurrence of stickiness and chromosome aberrations was prevented by adding excess cytidine to the 5-azacytidine solution.